On racing and cruising sailboats, devices for furling asymmetrical spinnakers, gennakers, all-purpose sails (“APS”) or similar type sails, have widely been used to furl sails prior to lowering, and similarly to hoist furled sails and unfurl for use. Examples of aspects of certain prior art furling-related devices are shown in U.S. Pat. Nos. 7,263,941 and 6,591,771 to Greghi and 6,318,285 and 5,463,970 to Hartlmeier et al. As shown in FIG. 1, a depiction of the primary components of a typical currently available furling system, these furling systems consist of a lower rotary drive unit 3A located near the bow connected to an anti-torsion cable 5A capable of transmitting a torque load to an halyard swivel 29A located near the top of the mast. The rotation of the lower rotary drive unit 3A is transmitted through the length of the anti-torsion cable 5A to rotate the lower portion of the halyard swivel 29A. The head 20 of a sail 27 attaches to the end terminal 69A at the top of the anti-torsion cable 5A or to the lower part of the halyard swivel 29A. The tack of the sail has a tack line 20 that is connected to the lower rotary drive unit 3A at a separate rotary tack swivel 21A so it does not rotate with the system until the very end of the furling operation. The sheets secured to the clew 22 are the third attachment to the sail; no others. The rotation force of the lower rotary drive unit 3A acts only on the top of the sail causing the head of the sail to furl first, so the sail progressively furls around the anti-torsion cable 5A. For this reason, this system is commonly known as a “top down furler.” Techniques have been developed by sailors to neatly furl the sail so it can be lowered to re-hoist and easily unfurled at a later time.
The lower rotary drive unit 3A is driven by a furling line 23, either wound on a spool or more often a sheave drive where the continuous looped furling line 23 wraps around the drive sheave. Textured features on the drive sheave, as well as a “V” shape of the sheave so the line pushes into the “V” as loads increase, grip the line to turn the lower drive unit when the furling line is pulled. The lower drive unit is also sometimes powered using a hydraulic or electric motor. The lower rotary unit and halyard swivel 29A are rotatably mounted in a bearing system to help reduce rotational friction from the fixed portions connected to bow 25 and halyard at masthead 26.
The lower rotary unit rotary tack swivel 21A provides a connection to the tack of the sail 27 that does not rotate with the drum or sheave drive in the lower rotary drive unit 3A. This allows the top of the sail to furl first because the tack can lag behind and remain stationary with the bow of the boat. In some cases this separate rotary tack swivel 21A is fastened directly to the lower rotary drive unit 3A. In other cases the rotary tack swivel 21A is tethered to the lower rotary drive unit 3 and rides on a shaft so its height can be adjusted. In either case ball bearings and races are used to reduce friction between the rotary tack swivel and the main rotary section with its pinned connection to the anti-torsion cable. Also, because the rotary tack swivel 21A is secured to the rotating portion of the lower rotary drive unit 3A, the loads on the sail tack are transferred to the main bearing system in the lower rotary drive unit 3A.
The anti-torsion cable 5A attaches to the top of the lower rotary drive unit 3A. When the lower rotary drive unit is rotated, the anti-torsion cable 5A rotates the halyard swivel. It is important that the halyard swivel 29A and the lower rotary drive unit turn at close to a 1:1 ratio. The anti-torsion cable 5A must be able to resist torsion and also be flexible enough to be coiled for storage after the furled sail is lowered. The longer the length of the anti-torsion cable, the more it has a tendency to twist, so that more rotations are required at the lower end of the anti-torsion cable compared to the upper end. Conventional anti-torsion cables 5A consist of braided low stretch fibrous materials such as Kevlar®, Dyneema® or Poly (p-phenylene-2,6-benzobisoxazole) (“PBO”), a rigid-rod isotropic crystal polymer. PBO fiber is a high performance fiber that has superior tensile strength and modulus compared to aramid fibers, such as Kevlar®, Technora® and Twaron®. Such materials are expensive to produce and sometimes layered with plastic strips to help increase resistance to torsion. Because the sail furls on the anti-torsion cable 5A, each separate asymmetrical spinnaker, gennaker and APS must have its own anti-torsion cable 5A.
The construction of the anti-torsion cable 5A consists of fibers woven and braided in two opposite helical or spiral directions around the length of the anti-torsion cable 5A. The materials used in the anti-torsion cable 5A have strength in tension but not in compression. Also the fibers used for reinforcement have negligible stiffness as an individual thread. When the anti-torsion cable 5A is not in tension, the individual fiber threads have space to move and constrict when torsion is applied, so there is twist. Anti-torsion stiffness is gained by tensioning the fibers in the weave so they become more densely compacted and there is nowhere for them to move. Tension increases the density of the weave thereby increasing the ability to transmit torque without twist. As a result, the anti-torsion cable 5A must be under very high tension before furling to increase the anti-torsion capability, so the cable will transmit the torque without twist or torsion.
To provide enough tension, sometimes halyards are led through a 2:1 block and tackle and or a large winch is used to achieve the tension required to transmit the torque at a 1:1 ratio between lower rotary drive unit 3A and the halyard swivel 29A. This high tension requires that hardware, such as bow sprits, their connections and halyard sheaves near mastheads, have higher strength capacity than hardware built for normal sail loading. The added weight to handle higher loads near the bow and masthead detracts from the sailboats overall performance and designers are always striving to make these areas lighter. This tension is very often applied before furling and not while using the asymmetrical spinnaker, so it requires a dedicated step. In many cases, before furling, the existing anti-torsion cables must be pre-twisted in order to furl because they do not have the anti-torsion capability, this thus requiring another dedicated step.
The ends of the anti-torsion cable 5A must be securely joined to an aluminum end terminal 9A due to the very high loads required for transmitting the torque using the anti-torsion cable 5A. Various fusing and bolting methods are used to secure the anti-torsion cable to the end terminal 9A. The connection of the end terminal 9A to the lower rotary drive unit 3A and the halyard swivel 29A consists of a fork and tang with a pin connection with locking mechanism, or other means, including two cylindrical metal parts pinned or bolted together to transmit the torque. They must be able to withstand high tension loads and torsion loads due to the requirement to have high loads to increase the torque capability of the anti-torsion cable.
Furthermore, due to the requirements to highly tension the anti-torsion cable 5A, bearings in the lower rotary drive unit 3A and halyard swivel 29A must be capable of handling higher loads than are required for sailing. As such, the lower rotary drive unit and halyard swivels require large diameter bearings and supporting races which add weight to the lower rotary drive unit 3A and the halyard swivel 29A. As an alternative, hardened steel bearings are sometimes used, requiring seals which add more friction to the rotational furling. In either case, the greater the tension, the more rotational friction is produced. Friction in the halyard swivel requires an anti-torsion cable with added torque transmitting capability to overcome this friction.
As such, there is a need for an improved system and components for a top down furling system. The improved system can include some or all of the following features and components:                a lower rotary drive unit that can easily drive the anti-torsion cable and handle the need to let the tack line lag behind the rotation of the anti-torsion cable without transferring the tack line loads to the bearings in the lower rotary drive unit;        a lower rotary drive unit with fewer moving parts thereby providing lower weight on the bow of the boat and lower manufacturing cost;        an anti-torsion cable that can transmit torque without being under high tension thereby reducing the required strength of all connecting components and bearing systems, hence reducing the weight and the expense of manufacturing the cable and all related furling parts of the system, and also simplifying the number of steps required to furl;        a quicker way to connect and disconnect the anti-torsion cable to the lower rotary drive unit and the halyard swivel so sails can be quickly connected to the lower rotary drive unit and the halyard swivel; and/or        a halyard swivel design that takes advantage of the lower load requirements of the anti-torsion cable and provides a way to easily attach the head of the sail without using heavy shackles.        